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Suppression of Il-12 transcription in macrophages following Fc gamma receptor ligation
M Grazia Cappiello1, F S Sutterwala, G Trinchieri
1Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Abstract:
Ligating Fc gamma R on macrophages results in suppression of IL-12 production. We show that Fc gamma R ligation selectively down-regulates IL-12 p40 and p35 gene expression at the level of transcription. The region responsive to this inhibition maps to the Ets site of the p40 promoter. PU.1, IFN consensus sequence binding protein, and c-REL: form a complex on this element upon macrophage activation. Receptor ligation abolishes the binding of this PU.1-containing activation complex, and abrogates p40 transcription. A dominant-negative construct of PU.1 diminishes IL-12 p40 promoter activity and endogenous IL-12 p40 protein secretion. Thus, the specificity of IL-12 down-regulation following receptor ligation lies in the inhibition of binding of a PU.1-containing complex to the Ets site of the IL-12 promoter. These findings provide evidence demonstrating for the first time the importance of PU.1 in the transcriptional regulation of IL-12 gene expression.
Insights
Fc gamma receptor ligation suppresses interleukin-12 (IL-12) production by inhibiting the transcription of its genes. This suppression is mediated by blocking the binding of a PU.1 transcription factor complex to the IL-12 p40 promoter region.
Area of Science:
- Immunology
- Molecular Biology
- Gene Regulation
Background:
- Macrophages play a critical role in immune responses, including the production of cytokines like IL-12.
- Fc gamma receptors (Fc gamma R) on macrophages are involved in immune complex recognition and signaling.
- IL-12 is a key cytokine in T-cell differentiation and innate immunity.
Purpose of the Study:
- To investigate the molecular mechanisms by which Fc gamma R ligation suppresses IL-12 production.
- To identify the specific regulatory elements and transcription factors involved in IL-12 gene expression modulation.
- To elucidate the role of the transcription factor PU.1 in IL-12 regulation.
Main Methods:
- Analysis of IL-12 p40 and p35 gene expression at the transcriptional level.
- Promoter deletion and mutation analysis to map inhibitory regions.
- Electrophoretic mobility shift assays (EMSAs) to study transcription factor binding.
- Use of dominant-negative constructs to assess the role of PU.1.
Main Results:
- Fc gamma R ligation selectively down-regulates IL-12 p40 and p35 gene expression transcriptionally.
- The Ets site within the IL-12 p40 promoter is crucial for this regulation.
- A transcription factor complex including PU.1, IFN consensus sequence binding protein, and c-REL binds to the Ets site upon macrophage activation.
- Receptor ligation disrupts the binding of this PU.1-containing complex, abrogating p40 transcription.
- Dominant-negative PU.1 reduces IL-12 p40 promoter activity and protein secretion.
Conclusions:
- Fc gamma R ligation inhibits IL-12 gene transcription by preventing the binding of a PU.1-containing complex to the IL-12 p40 promoter's Ets site.
- This study demonstrates the critical role of PU.1 in the transcriptional regulation of IL-12 gene expression.
- These findings provide novel insights into the immunomodulatory functions of Fc gamma receptors.
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